Conventional deterrence failed at Yeonpyeong because the ROK-U.S. alliance lacked credibility — and credibility is built from past actions (reputation), not from capacity on paper; Pyongyang had learned, from earlier unanswered provocations, that retaliation was not credible.

— In our words · Source: A Study on the Failure of Conventional Deterrence: The Case Study of the Bombardment of Yeonpyeong in 2010 (Jin Ki Lee)